## Fluids

#### Set mass flow to symmetry boundary

• Jimmyhan
Subscriber

Hi, this is Jimmy, I need some suggestion for my simulation. As we know, a part of the total structure is selected for simulation in order to save simulating time. So we have to set boundaries properly. In CFX three kinds of boundary setting wall, periodic interface and symmetry. I think the boundary setting is depended on which part do you selected from the total structure. But the problem is when all boundaries are symmetry boundary except wall, how can I set mass flow to the simulating part. Briefly say, if  I set the boundary as symmetry boundary how to set mass flow to this symmetry boundary?Good day, thank you for your reading.

• raul.raghav
Subscriber

Jimmy, so are you saying that you flow domain has no inlet and outlet? What do you mean by “all boundaries are symmetry boundary except wall”?

When you use symmetry boundary condition, there is zero flux across the defined surface. The normal velocity and the normal gradient of all the variables would be zero. So technically you cannot define a velocity or pressure at the symmetry plane. I hope that helps understand the boundary condition.

Symmetry boundary condition Fluent

To better understand the periodic boundary condition, refer:

Periodic boundary condition Fluent

• peteroznewman
Subscriber

Hey Jimmy,

I would slice it up with a hexagon and have three inlets and three outlets for simplicity.
I would slice it horizontally and use symmetry on the orange line and halve the mass flow rate at i.2.

I attached a Powerpoint inside a zip file if anyone else wants to sketch another idea.

• Jimmyhan
Subscriber

Thank you, Peter.  Your idea is great. I would like to try, but I really worry about meshing. Whatever, I appreciated your kindness.

• Raef.Kobeissi
Subscriber

Hi Jimmy,

Please update us with the result

Cheers

• Jimmyhan
Subscriber

I am sorry to let you guys know that the CFX version I used is a student version. When I followed Peter suggestion the mesh node is more than 512K limitation. So I can draw and make the mesh, but I cant use this method for simulation, unfortunately. Maybe you can give a new idea. Today, I still try other ideas and ask help from a guy which have the license, But his computer is very very slow...The really terrible thing is this geometry is the most simple one in 8 geometries I will estimate. Sometimes, I feel I am a dreamer but engineer, hahaha.